The Role of Soil C:N in Understanding On-Farm CO2 Emissions

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The soil Carbon-Nitrogen ratio (C:N) provides an overview of change in carbon and nitrogen stock in soil due to change in land use. However, a rational analysis of change in stock of carbon and nitrogen has not yet been used to understand carbon footprint from managed soils. This is the first study to propose the role of C:N ratio to understand on farm CO2 emissions from agriculture. Existing agricultural databases have high levels of uncertainty; we hypothesize that the use of scaling factors to estimate carbon footprint underestimate nutrient management in a watershed. Therefore, in this study on-farm CO2 emissions were simulated using a watershed-scale biogeochemical model called SWAT (Soil Water Agricultural Tool). Simulated physical processes were then coupled with IPCC guidelines for greenhouse gas estimation. A biological agricultural scenario was considered with a continuous corn–soybean–oats rotation using alfalfa and cereal rye as cover crops, conservation tillage using a LEMKEN cultivator, and a mix of conventional and biological fertilizers. The same crop rotation was assumed for a comparative conventional scenario without cover crop, intensive tillage and conventional fertilizers. Biological agricultural practice, showed a 25% reduction in carbon footprint than conventional practice. C-footprint from bio-based practice could be further reduced to 27% and 33% by adopting strip till and no till respectively. Results concluded that soil C:N is rich in nitrogen indicating residual nitrogen as the major source of N2O emissions. With the increase in soil C:N ratio, the on-farm emission decreased. Bio based approach had higher soil C:N ratio than conventional baseline scenario, however, higher soil C:N ratio for sustainable conventional practices were noted with the introduction of cover crop and application of lime.